1. Field of the Invention
The present invention relates to wet motor gerotor fuel pumps and, more particularly, to wet motor gerotor fuel pumps having motor shafts that must be lubricated.
2. Description of the Prior Art
While the fluid being pumped by a wet motor gerotor pump is normally available to lubricate the bearings supporting the armature shafts, it has been found that one of such bearings is often starved of sufficient lubricating fluid. Such starvation is most often related to the orientation of the pump, the upper bearing in a vertically oriented pump experiencing the most severe problems. In addition to orientation related lubrication starvation problems, the design of the bearing support walls, while theoretically allowing the introduction of lubricating fluid, may nevertheless effectively prohibit the flow necessary to lubricate the bearing and cool, i.e. carry away frictional heat generated by the shaft and bearing relationship. For example, in a vertically oriented pump, the upper bearing is normally in a region that is last to receive any fluid during starting operations. Moreover, should the starting operations be under conditions where the motor chamber is filled with vapor pressure that is not properly vented, the vapor pressure will build up in the small cavities surrounding the upper bearing, further deterring the flow of lubricating and cooling fluid thereto. Moreover, regardless of pump orientation, should a shaft end be rotatably mounted in a blind bore, a pocket may be formed between the bearings supporting the shaft and the bottom of the blind bore wherein vapor pressure, once present, builds up to permanently force out any fluid that attempts to lubricate the motor shaft and cool the surrounding bearing. In view of such design and orientation problems, the bearings supporting at least the upper end of the motor shaft, not mounted along a horizontal axis, have a known failure mode. The bearings supporting the lower end of the motor shaft normally being in the path of the incoming fluid are, therefore, adequately lubricated and cooled thereby.
A further problem with the prior art lubrication of bearings supporting the motor shaft of a wet motor gerotor pump is the congested nature of the outlet housing to include both support structure for the shaft end, outlet valving and ports, a commutator end support, brushes contacting the commutator, and structure for slidably supporting the brushes relative to the commutator. Such structure has heretofore limited the nature and extent of the ducting for lubricating and cooling the bearings.